As mentioned above, the blood test for Coeliac Disease is rather unreliable. I've been diagnosed Coeliac over 40 years - well twice actually. I'm 61 and when I was little, there were no tests for CD so if they suspected you had it, they would trial a GF diet and see if you started to get well. It was also believed at that time that it was a childhood illness that you would grow out of and I was put back on 'normal' food at around age 7. I had a very turbulent teenage time and wonder if this was probably down to eating gluten and when I got to early 20s, I noticed some foods definitely didn't agree with me. I asked the GP to test for CD and they agreed because my early years showed that I had already had it.
So they did a blood test which was negative, but I was sent for an endoscopic biopsy and this proved conclusively that I did have CD. At that time the tube they put down your throat was a lot wider than it is now too!
One of the most classic symptoms of CD is anaemia, so ask if you can have a blood test for that, then most typical symptoms would be tummy bloating (when I was little they called it Belsen belly as children looked very malnourished like Belsen children did, with a very distended belly) and what used to be termed 'explosive motions'. These are the main symptoms.
And as others have had, don't rely on being able to get gluten free food on prescription as many NHS trusts and Clinical Commissioning Groups are beginning to withdraw this choice and you couldn't get all GF foods on prescription anyway. Also many pharmacists have a block on quite a number of GF items because the delivery cost to the pharmacy is too expensive.
To have a successful result from a biopsy, you do need to have been eating gluten for around 6 weeks before the test. Gluten damages the silky fronds called 'villi' in the lining of the intestine and if you stop eating it the villi start to recover. So if you stopped eating gluten before the biopsy, they might not see any damage.
But if you feel well with no gluten in your diet, then stick with it